Storm water inlet pollution trap

ABSTRACT

Pollutants are captured at a particular point of entrance into a storm water runoff system, such as at curb inlets. An inventive device takes advantage of existing storage volume within storm water inlets and is installed therein with little or no retrofitting necessary to secure the device. Storm water enters the apparatus where water energy is reduced and flow length is increased, increasing water detention time and allowing for the removal of soil sediment, floating debris, hydrocarbons and other pollutants utilizing settling tendencies and trapping areas. A damping system reduces pollutant resuspension and redirects high flows away from deposited sediment.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of prior filed, copendingU.S. provisional patent application Ser. No. 60/200,694, filed 29 Apr.2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to a pollution controlapparatus, and, more specifically, to an apparatus for attachment to astorm water inlet, such as a curbside inlet, for collecting storm waterpollution, such as sediment, floating debris and floating residues, fromstorm water runoff.

[0004] 2. Background

[0005] It has been reported that forty percent of our nation's rivers,lakes and streams are considered unfit for fishing, swimming, drinkingor aquatic life. Urban streams have substantially more problems becausehigh sediment loads affect many aspects of water quality, includingwater temperature, pH, total suspended solids, total dissolved solids,nutrients, metals, pesticides, and bacteria. Sediment loads from landsundergoing urbanization are up to 50 times more than those in ruralareas. It is excessive sediment, generated as anthropogenic waste, thatoften overwhelms the “assimilative capacity” of a stream and damages itsbiological components.

[0006] A primary cause of diminished water quality is urban storm waterrunoff. Urban runoff is a pollutant that consists of soil sediment,floating organic matter, floating man-made debris, chemicals, and otherresidues. The quality of urban runoff is thus an important issue due tothe negative effects it can have on ecological systems and water bodyvolume. Urban runoff carries large amounts of soil sediment whichincreases the turbidity of water, causes siltation of reservoirs, lakesand ponds, and ultimately adversely impacts aquatic plants,invertebrates and fish.

[0007] One of the greatest contributors to sediment entering storm watersystems comes from construction sites, where soil is exposed and caneasily erode and be transported into the drainage system. The majorproblem at construction sites is the period of time that disturbedsurfaces lay exposed, more than a year at 25% of the sites. Most citieshave the authority to regulate construction sites to make sure they arecomplying with regulations to reduce the amount of sediment coming fromthe sites. Covering exposed soil, setting up filter fences and strawbales, reseeding exposed soil and using gravel at exits and entrancesare all practices used to reduce soil erosion from construction sites.

[0008] Soil can also be distributed throughout a city on rooftops and onstreets by wind. Having a combination of high winds and large amounts ofagricultural land in more rural areas sets up the conditions for largeamounts of soil to be deposited on streets throughout a city. The soilis then washed into the storm water system in a rain event.

[0009] Soil can also come from the thousands of vehicles that travel thestreets. Vehicles collect soil from back roads and alleys, thentransport it to the city streets, where the soil can easily be washedinto the storm water systems. Soil contributors come from many differentplaces, and the same is true with contributors of municipal trash anddebris that enters the storm water systems.

[0010] Municipal trash is especially difficult to eliminate because ofthe wide variety of contributing sources. Municipal trash has severalopportunities to slip through the sanitation removal system. Forexample, animals, weather, and people all add to the enormous amount oftrash that is available to be carried into a storm water system. Inaddition to sediment and municipal trash, natural debris like treelimbs, grass clippings, and leaves, contribute to the problems in stormwater systems.

[0011] There are many other sources and types of pollutants that enterurban runoff. Petroleum products, fertilizers, chemicals, pesticides,and fecal bacteria are all pollutants found in urban runoff. The keycontributor to all of these pollutants is man and his mishandling andmisuse of products.

[0012] Many cities are actively seeking procedures and devices that canimprove the quality of storm water runoff. The problem is currentlybeing addressed in two principal ways. First, most cities regulateconstruction sites. Regulation ensures that construction sites have theproper erosion control devices installed to limit the amount of soilcoming from a construction site, both from water flow and from trafficflow. Second, significant funds are expended on cleaning city streetswith sweepers and manually cleaning out storm water inlets. Due,however, to budget and manpower constraints only a minimal level ofmaintenance is generally performed, enough only to keep storm watersystems functioning.

[0013] The current control methods fall drastically short of meetingpollution control goals. Present methods do not stop any sediment ordebris present in runoff streams from entering and passing through thestorm water system nor do they serve to remove or filter any floatablecontaminants. In addition, current systems do not allow for an easy andefficient clean out method.

[0014] The optimum improvement to the quality of storm water runoffwould consist of eliminating the aforementioned pollutants whilemaintaining high flow rates to eliminate flooding potential, recognizingthat there will be an expected variation in the degree to which any orall of the pollutants can be removed and to what degree the flowabilityin the system can be maintained.

[0015] It is thus an object of the present invention to provide a devicethat will effectively remove a large portion of the pollutants enteringa storm water runoff system while maintaining a high level offlowability in the system.

[0016] It is a further object of the invention that the device be simpleto construct, install and maintain as well as effective in trappingpollutants entering storm water sewer systems.

SUMMARY OF THE INVENTION

[0017] These and other objects are achieved by capturing pollutants at aparticular point of entrance into a storm water runoff system, such as,for example, at curb inlets. The inventive device takes advantage ofexisting storage volume within storm water inlets and is installedtherein with little or no retrofitting necessary to secure the device.Storm water enters the apparatus where water energy is reduced and flowlength is increased, increasing water detention time and allowing forthe removal of soil sediment, floating debris, hydrocarbons and otherpollutants utilizing settling tendencies and trapping areas. A dampingsystem reduces pollutant resuspension and redirects high flows away fromdeposited sediment.

[0018] Thus, in accordance with the objects of the invention there isprovided a method for water detention within a storm water sewer systemto allow for the trapping and collection of soil sediment, floatingdebris, hydrocarbons and other pollutants wherein a waste water streamis routed to a housing suspended below a storm water inlet wherein,depending upon the amount of flow, the stream follows one of twopossible flow paths. In low flow conditions the stream is directed suchthat its flow length and retention time within the housing is increased,thus allowing for the settling out of sediment and for the capture offloating debris and residues. In high flow conditions the stream isdiverted to an alternate shorter flow path out of the housing so as notto cause a resuspension of collected sediment.

[0019] A preferred trapping device for use in accomplishing theaforedescribed method includes a two piece housing consisting of frontand back portions slidably received together to form a generallyrectangular structure to accommodate a common configuration of a stormdrain. The device may be shaped so as to conform to other common stormdrain configurations or may be specially adapted to fit particularapplications. Accordingly, the particular shape of the housing can bevaried as needed to complement, for example, round or square drains. Forillustrative purposes, the following description will refer as anexample to a device for use under a generally rectangular curb inlet.

[0020] A top, hopper-type portion of the device is provided with a lip,being appropriately sized and adapted to be engaged between the lip ofthe curb inlet grate and the ledge upon which the grate typically rests.The length of the device is such that it is suspended beneath the gratewithin the curb inlet so as not to impede water flow beneath thestructure.

[0021] Water flowing through the grate is directed by an upper surfaceof the housing into a first detention area within the housing whereupon,under low flow conditions, the water proceeds through a damper into asecond larger detention area defined by the walls of the housing. Thesediment laden water has a relatively long residency time in the seconddetention area, thus allowing sediments to settle out from the water.The damper serves to increase the flow length of the sediment ladenwater stream and minimizes resuspension of sediments contained in thesecond detention area. Flow between the first and second detention areasis controlled through the adjustment of the damper. In the preferredembodiment, the damper comprises overlapping plates and the degree ofseparation between the plates controls the flow rate between the firstand second detention areas. As the water level rises in the seconddetention area it climbs upward along the walls of the housing where iteventually advances through a fluid passageway located between the firstdetention area and the walls of the housing. The water exits the housingthrough apertures located in the housing walls. The exit points arevertically spaced at a point below the water head in the first detentionarea so that floating debris and residues are trapped in the firstdetention area above the exit points.

[0022] During high flow conditions, when the rate of water flow into thefirst detention area surpasses the maximum rate of flow through thedamper, water overflows the first detention area to be released throughthe exit points in the walls of the housing. In this manner,resuspension of the sediments captured in the second detention area isavoided.

[0023] The inventive device is maintained by periodic removal of thetrapped pollutants. Access is afforded to the interior of the devicethrough the removal of the curb inlet grate, whereupon the pollutantsare removed by vacuum suction or other means.

[0024] The inventive device is simple and has no moving parts that willwear out, break or reduce efficiency over time. It can easily be adaptedinto any existing curb inlet or other storm water inlet and optimizesstorage volume while maintaining a flow path long enough for adequateefficiency. Pollutant removal is easily accomplished, and the device isvery cost effective and manageable.

[0025] A better understanding of the present invention, its severalaspects, and its objects and advantages will become apparent to thoseskilled in the art from the following detailed description, taken inconjunction with the attached drawings, wherein there is shown anddescribed the preferred embodiment of the invention, simply by way ofillustration of the best mode contemplated for carrying out theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a perspective view of a general embodiment of thepresent invention.

[0027]FIG. 2 is an exploded view of the components of the device of FIG.1.

[0028] FIGS. 3A-G are partial cross sectional views of an upper portionof a general embodiment of the present invention.

[0029]FIG. 4 is a perspective view of the inventive device showninstalled in its typical environment.

[0030]FIG. 5 is a perspective view of the preferred embodiment of theinventive device.

[0031]FIG. 6 is a perspective view of the front piece of the device ofFIG. 5.

[0032]FIG. 7 is a perspective view of the back piece of the device ofFIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] The main objective of the preferred embodiment of the inventionis to remove soil sediment, floating debris, and a limited amount offloating residues from storm water runoff. The floating residues thatthe device addresses are primarily floating hydrocarbons deposited onstreets and parking lots from vehicular oil leaks. The floating debrisis generally a combination of man-made trash and organic material suchas leaves, grass clippings, and tree limbs. The trapping of soilsediment focuses on the larger sizes of silt and sand. Before explainingthe preferred embodiment in detail, however, it is important tounderstand that the invention is not limited in its application to thedetails of the construction illustrated and the steps described herein.The invention is capable of other embodiments and of being practiced orcarried out in a variety of ways. It is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and not of limitation.

[0034] Referring now to the drawings, wherein like reference numeralsdesignate identical or corresponding parts throughout the several views,and particularly referring to FIGS. 1-3, the inventive device 10, showngenerally in a fully assembled condition, has a front 12 and a back 14.The device 10 comprises a housing 16 consisting of two side panels 18,20, a back panel 22, and a front panel 24 to form a generallyrectangular structure. The device 10 may be of a unitary structure orcomprise a multi-piece design, such as the particularly preferredtwo-piece embodiment described in detail below. The purpose of FIGS. 1-3is to provide a general description of the salient features of theinvention.

[0035] One or more of the panels are provided with apertures 25 whichserve as water exit points. The size of the apertures 25 are calculatedto release the maximum flow rate known for the inlet to which it isattached. At the top portion of the device 10 there is an upper surfacecomprising a hopper 26 formed of a plurality of angled surfaces 28. Thehopper 26 is provided with a lip 46, being appropriately sized andadapted to be engaged between the lip of a curb inlet grate and theledge upon which the grate typically rests. The length of the device 10is such that it is suspended beneath the grate within the storm waterdrain so as not to impede water flow from the bottom of the drain intothe storm water system piping.

[0036] In addition to supporting the device 10 in a suspended positionunder the inlet grate, the hopper 26 and angled surfaces 28 function tolengthen the flow path of the device 10 and to direct water flowingthrough the grate into a first detention area 34. A set of vertical fins30 affixed at the terminus of the angled surfaces 28 extends the flowpath vertically to within the first detention area 34 while maintainingadequate dimensions between the side panels 18, 20 and front panel 24,the purpose of which will become evident from the ensuing description.The vertical fins 30 extend downward in the device 10 to a point belowthe apertures 25 in the side and front panels 18, 20, 24.

[0037] The first detention area 34 is created within the bounds ofdiverter 32, a pair of blockers 36 and damper 38. The diverter 32, shownformed from three segments, separates the first detention area 34 fromthe side and front panels of the housing. The diverter 32 extends abovethe level of apertures 25 in order than the water head in the firstdetention area 34 be maintained above the level of the apertures 25.This allows floating debris and residues to remain above the exit pointof the device and within the first detention area 34 under low flowconditions. The blockers 36 are fixed between the vertical fins 30 andthe side panels 18, 20 to prevent the flow of water around the diverter32 and through the apertures 25 and to provide added structuralintegrity. The diverter 32 may be tacked to side panels 18, 20 and frontpanel 24 for support. The damper 38, shown as overlapping plates 40, 42serves to separate the first detention area 34 from a larger seconddetention area 44. The height of the diverter 32 may be varied relativeto the aperatures 25 to alter flow characteristics.

[0038] Water flowing through the inlet is directed by angled surfaces 28at the top of the housing 16 into the first detention area 34 whereupon,under low flow conditions, the water proceeds through the damper 38 intothe second larger detention area 44. The sediment laden water has arelatively long residency time in the second detention area 44. Theallowable flow through the damper 38 may be adjusted, but in thepreferred embodiment the distance between the plates 40, 42 comprisingthe damper is about 2.5 to 3 inches which, considering the otherdimensions of the structure, allows for a flow rate of approximately onecubic foot per second (cfs). As the water level rises in the seconddetention area 44 it climbs upward through a fluid passageway 45provided between the diverter 32 and side and front panels 18,20,24. Theoutflow pattern from the second detention area 44 is shown with a dottedarrow in FIG. 3F. The rising water from the second detention area 44leaves the device through apertures 25.

[0039] During high flow conditions, when the rate of water flow into thefirst detention area 34 surpasses the maximum rate of flow through thedamper 38, water overflows the first detention area 34 over diverter 32to be released through the apertures 25 in the side and front panels ofthe housing 16. The outflow path under high flow conditions isillustrated in FIG. 3F with a solid arrow. Having this alternate flowpath for high flow conditions reduces resuspension of the sediment thathas settled out of the water within second detention area 44 by limitingthe amount of flow that passes through the second detention area duringperiods of high volume runoff.

[0040] The inventive device is maintained by periodic removal of trappedpollutants. Access is afforded to the interior of the device 10 throughthe removal of the inlet grate, whereupon the pollutants may be removedby vacuum suction, scooping or other means. It is contemplated that atrap door may be designed into the damper 38, such as a door having ahandle and a magnetic latching system, to provide easier access into thesecond detention area 44. The bottom of the housing 16 might also berounded for ease of maintenance. It is further contemplated that weepholes might be located along the side of the device 10 (covered by ashield) allowing for standing water to escape the device withoutreleasing sediment.

[0041] FIGS. 5-7 illustrate a particularly preferred two piece device.The two piece device consists of a front piece 100 and a back piece 102.The back piece is provided with a tube 104 along each of its verticalmating edges into which the rod 106 of the front piece 100 may beslidably received. FIG. 6 best illustrates the structure of the frontpiece 100 wherein, as it has been previously described, there isprovided hopper 126, vertical fins 130, lip 146, apertures 125, diverter132, blockers 136 and damper 138.

[0042] As shown best in FIG. 7, back piece 102 possesses two plates 140,142 which, along with plate 141 in the front piece 100, comprise thedamper 138. It will be noted that plate 140 in the back piece 102 mateswith plate 141 in the front piece 100. The degree of separation betweenplate 140 and plate 142 controls the flow rate from the first detentionarea 134 to the second detention area 144.

[0043] Typical installation of the device will be described in relationto FIG. 4. The device is dimensioned so that its lip may be engagedbetween the storm water inlet grate 48 and the ledge 50 upon which thegrate 48 rests. The length of the device is such that it is suspendedbeneath the grate 48 within the storm water drain 52 so as not to impedewater flow from the bottom of the drain 52 into the storm water pipingsystem 54. With reference to the preferred embodiment described above,it would be typical to remove the grate 48 in order to first insert theback piece 102 of the device through the opening into the drain 52,whereupon the lip of the back piece is positioned upon a ledge on thecurb side of the drain 52. It is common that the curb side of the drainis inset somewhat so that what will be seen from above after insertionof the back piece are basically the mounting tubes 104. The front piece100 is then similar inserted through the opening so that its mountingrods 106 are slidably received in tubes 104 and the lip of the frontpiece is positioned upon a ledge on the street side of the drain 52. Thegrate 48 is then replaced, and the device is thus suspended foroperation. Other suspension means such as hooks, hangers and otherfasteners also may be utilized if so desired.

[0044] It should be further recognized that the aforedescribeddescription and drawings refer to a device for installation on the leftside of a curb inlet. Center and right side devices are, of course,within the scope of the invention.

[0045] The type of material used in the construction of the device maybe varied according to strength, durability and thickness requirementsand the overall acceptable cost of manufacture. A prototype device wasconstructed of plexiglass but it is anticipated that a low cost nylonmolded product could be used for commercialization, with other suitablematerials including fiberglass, metals or heavy duty plastics such aspolyethlene.

[0046] The details of the construction illustrated and described abovein connection with the preferred embodiment of the invention may bemodified by one skilled in the art to achieve particular desiredoperating parameters and pollutant removal efficiencies. The pollutantsthat are being addressed can only be effectively captured within a givenrange of parameters. The design parameters include: concentration ofpollutant, flow rate of runoff, and limited flow restrictions.Pollutants have different environmental impacts depending on theirconcentration and potency. For example, 100 grams of soil sediment willnot have the same environmental impact as 100 grams of motor oil.Because of the different environmental impacts, water quality standardsare set in place by organizations such as the Environmental ProtectionAgency (EPA) to monitor storm water runoff quality. The storm water ismonitored for pollutants that exceed set concentrations. One quart ofmotor oil has the potential to contaminate 250,000 gallons of waterbased on the water quality set by the EPA (City of Laguna, 2000).Accordingly, small amounts of motor oil or other hydrocarbons have thepotential to cause large environmental problems.

[0047] For example, the components of the device may be arranged anddimensioned to vary the efficiency of removing soil sediment from stormwater. Removing soil sediment is a process that is governed by Stoke'slaw. Stoke's law is an equation used to determine the settling velocityof particles based off of the particle size:

Vs={fraction (1/18)}[(d ² /v)*(SG−1)],

[0048] wherein

[0049] Vs=settling velocity;

[0050] d=particle diameter;

[0051] g=gravitational constant;

[0052] v=kinematic viscosity; and

[0053] SG=specific gravity of the particles.

[0054] Using a SG of 2.65 and assuming quiescent water at 68° F., theStoke's law equation reduces to: Vs=2.81d². Using the following USDAtable for particle sizes <2 mm in diameter, the resulting settlingvelocity for various classes of sediment can be calculated. CLASS SIZE(diameter) Very coarse sand 2.0-1.0 mm Coarse sand 1.0-0.5 mm Mediumsand 0.5-0.25 mm Fine sand 0.25-0.10 mm Very fine sand 0.10-0.05 mm Silt0.05-0.002 mm Clay <0.002 mm

[0055] Knowing the calculated settling velocities enables furthercalculations to be made to determine what theoretical particle size canbe removed for a given flow length and flow rate. The maximum flow ratesfor typical curb inlets are given below. max flow flow rate flow rate #of curb inlets rate(cfs) curb(cfs) grate(cfs) 1 4.1 2.5 1.6 2 8.2 5 3.2

[0056] The max flow rate for a single inlet is equal to 4.1 cubic feetper second (cfs). Using the maximum flow rate in units of cubit feet persecond and dividing the flow rate by the flow area, given in feetsquared, the flow velocity can be calculated having units of feet persecond. After obtaining the flow velocity, a flow length can beestablished that will allow the time needed, based off the settlingvelocity, for a certain particle size to settle out of the flow path.

[0057] To determine the actual particle size that will settle out of theflow, one skilled in the art will know to determine how far from themain flow path the particle will have to be before it will settle out ofthe flow stream. The size of the device, constrained by the curb inletopening, also must be taken into account which limits the use of optimallonger flow lengths. A flow capacity that will allow efficient sedimentremoval without adversely affecting resuspension must also bedetermined.

[0058] Calculations can be made to size various parts to achieve therequired flow rates. The required flow rates are based on the amount ofmaximum flow the device must pass and the amount of flow the device willdirect through a longer flow path. The flow calculations may be made,for example, using the following weir and orifice flow equations:

[0059] Weir Flow

Q=CLH ^(({fraction (3/2)})),

[0060] wherein

[0061] Q=flow rate in cubic feet per second;

[0062] L=weir length in feet; and

[0063] H=head in feet.

[0064] The weir flow calculations are used to determine the length andheight that is needed to pass the max flow and the redirected flow.

[0065] Orifice Flow

Q=C′A(2gH)^((½)),

[0066] wherein

[0067] Q=flow rate in cubic feet per second;

[0068] A=cross-sectional area of the orifice in square feet;

[0069] g=gravitational constant;

[0070] H=the head on the orifice; and

[0071] C′=the orifices coefficient.

[0072] The orifice equation is used to calculate the height, given alength, which will pass the redirected lower flow.

[0073] With reference to the trapping of floating pollutants andfloating debris, the construction of the components of the device may bearranged and dimensioned to vary the size and placement of storage areasto allow for the inflow of floating pollutants and debris but tootherwise separate the storage areas from the direct flow path of thewater to avoid the submergence of the pollutants into the water stream.

[0074] The present invention will be further understood with referenceto the following non-limiting experimental example.

EXAMPLE

[0075] A full-scale prototype was designed to simulate hydrauliccharacteristics, pollutant removal efficiency, and maximum flowcapacity. The prototype testing was divided into two specific setups.First, a setup was used that allowed soil to be introduced into thedevice at a known concentration at relatively low flows ranging from 0.2to 0.6 cubic feet per second. A second setup was used to introduce highflow rates ranging from 3 to 4.1 cubic feet per second. The second setupdid not introduce additional soil; it was used primarily to insure thatthe maximum design capacity would pass through the device.

[0076] Before the prototype testing proceeded, many testingconsiderations were addressed. The considerations included theconcentration of the soil and water mix, the flow rates, the duration ofa testing event, the water entrance conditions, and the types of soilthat would be introduced to the mix. A concentration of 3000 mg/l wasdetermined for the soil and water mixture. The concentration of 3000mg/l was determined based earlier studies in which samples ofsediment-laden water were collected and 3000 mg/l was the maximumconcentration encountered.

[0077] To address flow rates, an assumption of a critical flow rate wasmade. The critical flow rate is the flow that allows adequate sedimentremoval without resuspending the settled particles. A critical flow rateof 1 cfs was used. This flow rate governed the equations used tocalculate the dimensions of the prototype. The dimensions, calculatedusing 1 cfs as the critical flow, are the dimensions of orifices andweir heights that restrict the flow through the sediment detention areato under 1 cfs. Test flows of 0.2, 0.4, and 0.6 cfs were used in thesediment laden water test. These flows were used because they representthe target range for most efficient sediment capturing, and the sedimentladen water test was restricted by a maximum of 0.7 cfs. The flow of themaximum capacity test was simply placed at the maximum design flow of4.1 cfs to insure the device could pass the maximum flow.

[0078] The duration of a testing event was calculated based upon ofthree pieces of data. First, the maximum flow encountered by a singlecurb inlet is 4.1 cubic feet per second (cfs). Second, the assumptionwas made that the maximum flow was encountered during a one hour, onehundred-year flood event. Third, the amount of runoff needed forwash-off is 0.2 inches. The one hour, one hundred-year flood eventproduces an intensity of 4.1 inches per hour (Haan, Barfield, Hayes,1994). To produce a flow of 4.1 cfs, an intensity of 4.1 inches per hourmust be distributed over 0.99 acres. Using the calculated area, the 0.2inch wash-off amount, and a predetermined test flow rate, the durationof a test event can be calculated. The duration calculated is theduration needed to produce the volume of water that would be producedfrom 0.2 inches of rainfall over the calculated area with the givenconcentration of 3000 mg/l.

[0079] The sediment-laden water was introduced to the device using amockup of a curb inlet. The mockup was used to insure that entranceconditions were similar to real world conditions. The water wasintroduced into a cavity that would distribute a gradient of sheet flowwith the deepest area being next to the curb and the shallow areaextending away from the curb.

[0080] There were two types of soil tested, with one of the soils beingintroduced with two different characteristics. The first soil typetested was a red clay soil. The soil was prepared from a stockpile ofsoil. It was sieved using a # 8 sieve. The process of sieving eliminatedlarge aggregate, which aided distributing the proper rate of soil intothe water flow. The red clay soil was introduced at a moisture contentof 1% and at a moisture content of 10.7%. The difference in moisturecontent introduced a variance in the amount of aggregate the soilspossessed. The amount of aggregate effected the dispersion of the soilin the water. An increase in dispersion reduces the capturing efficiencyof the device because the effective particle size is reduced. The secondsoil tested was a sandy soil. The sandy soil was introduced to comparetwo very contrasting soil types.

[0081] The testing procedure for the sediment-laden water was a 6-stepprocess. The first step was to determine the soil moisture content (MC)of the soil sample. The soil moisture data is important in determiningthe mass of soil that needs to be introduced into the water. In order toan equivalent weight of dry soil, it takes more soil at a highermoisture content than soil at a lower moisture content. Theconcentration of 3000 mg/l is equivalent to 3000 mg of dry soil (0% MC)in one liter of water. Knowing the soil moisture content allows the massof soil to be adjusted to allow for the proper concentration. The secondstep was to calculate the flow time and amount of soil to introduce foreach flow rate. For each flow rate (0.2, 0.4, and 0.6 cfs), the totalvolume of water used and the total mass of soil used remains constant.The variables in the test were the duration and rate of soilintroduction. The third step was to place the device onto the scalesthat measure the change in weight of the device. The scales and devicewere then placed in position under the curb mockup and the device wasfilled with water and weighed. The fourth step was to calibrate the flowof water using a combination of a known size orifice plate and itscorresponding manometer differential. For a given size orifice plate, avalve can be adjusted that changes the manometer differential. Once atarget differential was reached that corresponds to the test flow rate,the test was ready to begin. The fifth step was to introduce soil at thegiven rate for the calculated duration. The soil was introduced into thewater flow 30 ft. before the device. The 30-foot distance allowed thesoil to become adequately mixed before it entered the device. The soilwas metered into the device by introducing a known mass of soil into thestream every minute for the duration of the test. The final step was tostop the flow and let the water drain to the same level as measuredpreviously. When the water was at the previously measured level, theweight of the device was measured.

[0082] Using the sediment-laden setup, other properties of the devicewere examined. The removal of floating pollutants was anotherperformance characteristic the device was designed to address. Tosimulate motor oil as an environmental pollutant, mineral oil was placedinto the water flow. The device is designed to keep the floating residueout of the direct flow path. The mineral oil was placed into the flowstream then the flow rate was increased from 0 cfs until the turbulencebecame to high to capture the oil. When the turbulence became too highthe oil was submerged into the flow path and exited the device. Thethreshold for capturing oil was found to be 0.5 cfs.

[0083] Floating debris (domestic trash and grass clippings) was alsointroduced into the device to allow visual inspection of the flowcharacteristics of the floating debris. Much of the floating debris wassuccessfully captured in the device. The flow path allows for largerdebris (3″), to pass into the storage area, but the outlet from thestorage area is reduced to 1 inch.

[0084] The testing procedure for the maximum flow capacity was set up totest two characteristics. The first, and primary, goal was to insure thedevice could pass the maximum design flow of 4.1 cfs. The second goalwas to see how maximum flow conditions affect previously settledparticles. The testing was set up in a channel that allowed theintroduction of high flows. Once the device was lowered into thechannel, sand particles were placed in the bottom of the device to seewhether the sand particles would become resuspended. After the devicewas filled with sand, a flow of 4.1 cfs was introduced to the device.The flow was maintained for 10 minutes. The final procedure was to drainthe device and visually insure that no sediment was lost during highflows.

Experimental Results

[0085] Five (5) different sediment-laden test were run under variousconditions. The following table is a summary of the data collected fromthe sediment-laden tests. After each test, a change in weight was foundby subtracting the final weight from the initial weight. The change inweight is proportionally related to the mass of soil collected. There isa difference because the soil particles that displace the water andwater have different densities. The conversion from the change in weightto the actual mass of soil collected can be calculated from thefollowing equation:

Weight of soil trapped=ΔW * (SGsoil/(SGsoil−SGwater)),

[0086] wherein

[0087] SG=specific gravity;

[0088] SGoil=2.65; and

[0089] SGwater=1.

[0090] Particle densities for most mineral soils vary between the narrowlimits of 2.60 to 2.75 g/cm³. A particle density of 2.65 may be assumedif the actual particle density is not known (Brady & Weil, 1999). Clayand sand samples were measured by mass and placed in a known volume ofwater to calculate the particle density. Particle density was calculatedon the sand and clay soil samples, and the densities ranged from 2.54 to2.66 g/cm³. Since there was such a narrow range in densities, theassumption of 2.65 g/cm³ was used as the particle density for both soiltypes. SOIL FLOW DURATION MASS OF SOIL TEST # TYPE RATE (cfs) (min)INTRODUCED MC soil 1 WET CLAY 0.6 15.40 107.5 10.73% 2 WET CLAY 0.433.25 149.0 10.73% 3 WET CLAY 0.2 50.00 111.5 10.73% 4 DRY CLAY 0.415.00  68.4  1.00% 5 SAND 0.4 16.60  62.7  2.32% CONCENTRA- MASS OF TIONDELTA WEIGHT MASS OF SOIL TEST # DRY SOIL (mg/l) OF DEVICE TRAPPED %EFFICIENCY 1 95.97 2772.9 50 80.30 83.00% 2 133.01 2669.9 66 106.3079.00% 3 99.5 2656.4 45 72.50 73.00% 4 67.72 3013.3 9 14.50 21.00% 561.25 2462.7 32 51.52 84.00%

[0091] The particle size distribution of the soil entering the devicecompared to the particle size distribution that remains in the devicecan be a very instrumental comparison. Knowing the capability of thedevice on a particle size basis enables the efficiency of the device tobe projected to a multitude of soil types.

[0092] One procedure for conducting such a particle size analysisinvolves passing a measured amount of a soil sample (such as 65 grams ofsilt or clay soil or 115 grams of sandy soil) through a #4 and #10sieve, whereupon the mass of the soil retained is measured and recorded.The soil that passes through the #10 sieve is soaked in a solution ofsodium hexametaphosphate solution for 16 hours to aid in the dispersionof soil aggregate. The solution is then added to a glass sedimentationcylinder and demineralized water is added until the total volume isequal to 1000 ml. The 1000-ml solution is stirred to ensure theparticles are adequately dispersed and the hydrometer is immediatelyplaced into the solution. Hydrometer readings are taken at 15, 30, 60,and 120 seconds and at 5, 15, 30, 60, 240, and 1440 minutes. Thehydrometer and sieving procedures produce values that are usable tocalculate particle sizes in mm and the percentage of finer particlesizes contained in the sample.

Device Maintenance

[0093] The maintenance on any single device can vary greatly dependingon a number of variables, including sediment concentration and rainevents and intensities. For example, Oklahoma City encompasses an areaof 650 square miles. Within this area, there are approximately 200,000curb inlets. Over this large area, a rain event may only affect certainportions of the area. Of the area effected by a rain event, there couldbe a variety of activities that could alter the concentration of soilparticles flowing in the water. Construction sites, gardening, muddyroads, and the amount of impervious versus pervious ground candrastically change flow conditions and concentrations. The maintenanceschedule will simply be an approximation using the following parameters:weather data collected from the Oklahoma City area, an averageconcentration of 3000 mg/l of soil particles in the run off water, andthe requirement of 0.2 inches of runoff to wash off a developed area(thus runoff exceeding the 0.2 inches of rainfall is consideredrelatively free of sediment). The final parameters are the drainage areaand the storage volume of the device. Using these parameters an expectedfilling time of the device can be calculated. The filling time alsotakes into consideration that organic matter will consume a portion ofthe volume.

[0094] To illustrate, soil samples were collected from existing curbinlets. These soil samples were analyzed for both particle size analysisand percent organic matter. Four samples were collected from theOklahoma City area. The four samples were placed in an oven for 4 hoursat 105° F. to remove moisture from the samples. After the soil was dry,it was weighed. The dry soil sample was placed in the muffle furnace at550° C. for 24 hours. The muffle furnace was used to burn off theorganic matter. The soil sample was weighed again, and the differentialin weight corresponded to the loss of organic matter. The four sampleshad an average of 11.75% organic matter. Soil particles have a particledensity of 2.65 g/cm³ and organic matter has a particle density of 1.1g/cm³ (Brady & Weil, 1999). Using these two densities, a weightedaverage of particle densities was calculated:

[(88.25*2.65g/cm ³)+(11.75*1.1g/cm ³)]/100=2.47 g/cm ³

[0095] The soil and organic matter that will fill the device willaccordingly possess an average particle density of 2.47 g/cm³. The 3000mg/l is the concentration of suspended particles in solution, so theaverage density of the suspended particles is estimated at 2.47 g/cm³.

[0096] The preferred inventive device has a volume of 8 cubic feet. Theamount of time needed fill the 8 cubic feet storage volume is dependenton the number of rain events that exceed 0.2 inches of runoff per year,as well as the area that each inlet services, the concentration of thesuspended particles in the run-off, and the trapping efficiency of thedevice. The number of rain events that exceed 0.2 inches of runoff isdependent on the curve number that best represents an urban area. Usinga conservative curve number of 95 allows for the amount of rain neededto produce 0.2 inches of run-off (the wash off amount). Turn now to theformula:

Q=(P−0.2S)²/(P+0.8S),

[0097] wherein

[0098] S=(1000/CN)−10;

[0099] P=accumulated precipitation (inches);

[0100] S=parameter;

[0101] Q=runoff (inches); and

[0102] CN=curve number (95 for a conservative # for urban areas).

[0103] Runoff begins after 0.2S of rainfall has fallen. Using theequation, it takes 0.52 inches of rainfall to initiate runoff. Using thevalue of 0.52 inches, we examine previous weather data to see how many0.52 inch rainfall events occur each year. Every 0.52 inch rainfallevent will not produce the concentration of 3000 mg/l because it takes asignificant amount of time between events to accumulate the particles toproduce that concentration.

[0104] As further example, the Oklahoma City area incurred approximately40 rain events over 0.5 inches between 1997 and 1999. Although many ofthe events were not spaced far enough apart to allow adequate time for abuild up of sediment, all 40 events were used in the approximation toensure a conservative estimate on device fill up time.

[0105] The service area of a single curb inlet was previously calculatedfrom the maximum of 4.1 cfs delivered during a 100 year flood event. Theservice area is thus calculated to be 43200 feet squared. Refer now tothe following data and formulae:

[0106] SERVICE AREA=43200 ft²

[0107] SOIL DENSITY=2.47 g/cm³

[0108] STORAGE VOLUME=8 ft³

[0109] RAIN EVENTS/YEAR=13.3 events/year

[0110] CONCENTRATION=3000 mg/l

[0111] WASH OFF AMOUNT=0.2 inches

[0112] EFFICIENCY=65%

cm ³/year=[(0.2in)(1ft/12in)(43200 ft ²)(1 liter/0.0353 ft ³)(3g/liter)(13.3 events/year)]/[(2.47g/cm ³)]

SEDIMENT ENTERING THE DEVICE(cm³/year)=3.29 E ⁵=11.64ft ³/year

SEDIMENT RETAINED IN DEVICE=(11.64 ft ³/year)(0.65 efficiency)=7.6 ft³/year

[0113] Using conservative values for both the curve number and thenumber of wash off events produces a volume of sediment per year that ismore than what should be expected. The volume of sediment trapped peryear was approximately 7.6 ft³ /year, and the device has a holdingcapacity of 8 ft³. Dividing the holding capacity by the expectedsediment volume per year produces a fill up time of approximately oneyear.

[0114] While the invention has been described with a certain degree ofparticularity, it is manifest that many changes may be made in thedetails of the process of assembly without departing from the spirit andscope of this disclosure. It is understood that the invention is notlimited to the experimental methods set forth herein for purposes ofexemplification.

What is claimed is:
 1. A storm water inlet pollutant trap for managing awater flow through a storm drain and extracting pollutants therefrom,comprising: a housing adapted to be suspended below a storm water inlet,said housing including therein: an upper surface to direct the waterflow; a first detention area at an upper portion thereof into which thewater flow is directed; a second detention area below said firstdetention area; a damper separating said first detention area from saidsecond detention area; at least one aperture positioned at least partlybelow the level of said first detention area; and a passageway leadingfrom said second detention area to said aperture; wherein under low flowconditions the water flow proceeds from said first detention areathrough said damper into said second detention area and ultimatelythrough said passageway to exit via said aperture; and wherein underhigh flow conditions the water flow bypasses said second detention areaby overflowing said first detention area to exit via said aperture. 2.The storm water inlet pollutant trap according to claim 1, wherein saidhousing comprises a two piece structure.
 3. The storm water inletpollutant trap according to claim 1, wherein said damper comprisesoverlapping plates.
 4. The storm water inlet pollutant trap according toclaim 1, wherein said housing is generally rectangular in shape.
 5. Thestorm water inlet pollutant trap according to claim 1, wherein saidupper surface empties into said first detention area at a point belowthe level of said aperture.
 6. A method for managing a water flowthrough a storm drain and extracting pollutants therefrom, comprising:routing the water flow to a housing suspended below a storm water inlet;under low flow conditions, routing the water flow along a first flowpath into a first detention area in said housing and then through adamper into a second detention area and ultimately through a passagewayto exit via an aperture in said housing; and under high flow conditions,routing the water flow along a second flow path bypassing said seconddetention area by overflowing said first detention area to exit via saidaperture.